Many types of input devices may be used to provide input to computing devices, such as buttons or keys, mice, trackballs, joysticks, touch screens and the like. Touch screens, in particular, are becoming increasingly popular because of their ease and versatility of operation. Typically touch screens can include a touch sensor panel, which may be a clear panel with a touch-sensitive surface, and a display device that can be positioned behind the panel so that the touch-sensitive surface substantially covers the viewable area of the display device. Touch screens allow a user to provide various types of input to the computing device by touching the touch sensor panel using a finger, stylus, or other object at a location dictated by a user interface (UI) being displayed by the display device. In general, touch screens can recognize a touch event and the position of the touch event on the touch sensor panel, and the computing system can then interpret the touch event in accordance with the display appearing at the time of the touch event, and thereafter can perform one or more actions based on the touch event.
Touch sensor panels can be formed from a matrix of row and column traces, with sensors or pixels present where the rows and columns cross over each other while being separated by a dielectric material. Each row can be driven by a stimulation signal, and touch locations can be identified through changes in the stimulation signal. Typically, a touch location is sensed based on an interference of the stimulation signal, such that a touch location may correspond to a location where the stimulation signal is the weakest. Touch sensor panels may generally be configured to detect touches from a user's fingers, which generally have a large surface area that contacts the touch sensor panel to disturb the stimulation signal sufficiently for touch location to be recognized. However, because of this configuration a stylus that includes a tip with a touch surface with a smaller surface area than a user's finger tip, may not sufficiently disturb the stimulation signal in order for the touch sensor panels to detect a touch location.
Furthermore, in some instances it may be desirable for input devices, such as styli, to be able to transfer data, in addition to the touch location data, to the touch screen. However, due to noise sources, and the capacitance coupling arrangement of typical touch screens, data transfer through a touch screen interface may be unreliable.